Re: (gcd -2) -> -2

[Mikael Djurfeldt]

2008/8/12 Neil Jerram <address@hidden>:
> 2008/8/12 Bill Schottstaedt <address@hidden>:
>> gcd is supposed to ignore factors of -1.
>
> According to?  (I'm not suggesting that you're wrong.  I'd just like
> you to be precise about your references.)

R5RS:

6.2.5 Numerical operations

 -- library procedure: gcd n1 ...,
 -- library procedure: lcm n1 ...,
     These procedures return the greatest common divisor or least common
     multiple of their arguments.  The result is always non-negative.

     (gcd 32 -36)                           ==>  4
     (gcd)                                  ==>  0
     (lcm 32 -36)                           ==>  288
     (lcm 32.0 -36)                         ==>  288.0  ; inexact
     (lcm)                                  ==>  1

>> "<" is restricted to reals -- a complex arg should be an error.
>
> Again, is that specified?
>
> Mathematically, I can't help wondering about Lim(x + iy) as y -> 0.
> Or, in Scheme terms, about inexact numbers.  Does inexactness in
> Scheme pertain only to the real dimension?

Mathematically, < doesn't have a meaning if its arguments complex,
i.e. if y above isn't exactly zero.  In Scheme terms, I guess one has
to consider a number real if the imaginary part is 0.0 even though it
is an inexact real number...